1. Field of the Invention
This invention relates to thermoformable polymeric foams and their use in shaped composites. More particularly, the invention is directed to the formation of shaped polyisocyanurate foam parts, especially panels, which have a wide range of uses, such as in the interior of motor vehicles, aircraft, ships and other transport means, and of both residential and commercial buildings.
2. Description of the Prior Art
The preparation of cellular polymeric molded parts, such as those involving polyurethane and polyisocyanurate foams, is well known. The resulting shapes may be advantageously used in a broad range of applications, e.g., as interior finishing materials in the railway, automotive, and aircraft industry, and in the building industry.
Both the polyurethanes and polyisocyanurates can be made by reacting a polyhydroxy-compound with a polyisocyanate, with a greater proportion of the polyisocyanate being used in the manufacture of the polyisocyanurates to make the latter highly cross-linked and therefore characterized by high compressive strength and a much greater heat and flame resistance than the polyurethanes. Unfortunately, the wide field of application potentially available to the polyisocyanurate foams by virtue of these improved properties is severely offset by their brittleness, which has impeded their being thermoformed into useful molded parts.
While there have been attempts to reduce the brittleness of polyisocyanurate foams and make them the foams of choice in thermoforming processes (see, e.g., U.S. Pat. No. 4,129,697), they are still regarded as unsatisfactory for practical use. For example, the polyisocyanurate foams of U.S. Pat. No. 4,129,697, which are synthesized predominantly from distilled diphenylmethane-4,4'-diisocyanate, are economically disadvantageous because of their high content of this relatively expensive isocyanate component. Accordingly, there is still a need for an economical polyisocyanurate foam whose properties qualify it for use in interior molded parts and which can be formed into such parts in an efficient and inexpensive manner.